... it would explain the connection between the Heart-Shaped Herb and Vibranium ...

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So if M'Baku had won the challenge near the start of the film, he would have rejected the herb? I suppose that's possible, but the movie never came close to even implying that, let alone stating it.

Not explicitely but, at the beginning of the movie, the Jabari were the only ones among the five Wakandan tribes who rejected the leadership of the Panther tribe.

Bast, the Panther God(dess), is explicitely connected to the Heart-Shaped Herb in the movie.

Not only the Heart-Shaped Herb gives panther-like powers to its consumer but it allows him to have access to an Astral plane populated by the panther spirits of the former kings of Wakanda (or so it seems ... Killmonger only saw his own father and, even though he was the brother of T'Chaka, Killmonger's father had not been a Black Panther himself, but both Killmonger & his father still belonged to the lineage of the Panther tribe).

M'Baku saw the death of T'Chaka as an opportunity to overthrow the rule of the Panther tribe over Wakanda because, during the ritual combat, T'Challa no longer had access to the powers of the Black Panther given by the Herb.

M'Baku would have renounced his commitments to the Gorilla Cult by consuming the Herb for his own benefit.